1. Field of the Invention
This invention relates to a process for the preparation of phosphorus-vanadium mixed oxide catalysts useful in the production of maleic anhydride by the oxidation of nonaromatic hydrocarbons. More particularly, this invention is directed to a process for the preparation of phosphorus-vanadium mixed oxide catalysts useful for the partial oxidation of nonaromatic hydrocarbons in the vapor phase with molecular oxygen or a molecular oxygen-containing gas to produce maleic anhydride in excellent yields.
Maleic anhydride is of significant commercial interest throughout the world. It is used alone or in combination with other acids in the manufacture of alkyd and polyester resins. It is also a versatile intermediate for chemical synthesis. Significant quantities of maleic anhydride are produced each year to satisfy these varied needs.
2. Description of the Prior Art
The preparation of phosphorus-vanadium mixed oxides and their use as catalysts in the production of maleic anhydride is known. As an example, U.S. Pat. No. 4,085,122 discloses a process which involves a salt of tetravalent vanadium, dissolved in an aqueous, non-oxidizing acid solution, with orthophosphoric acid. After the solution is concentrated, the vanadium salt complex is precipitated by adding water. The precipitate is collected, dried, formed into the desired form, and subjected to a heat treatment of at least 300.degree. C. to produce the catalyst.
U.S. Pat. No. 3,293,268 teaches a process of oxidizing saturated aliphatic hydrocarbons to maleic anhydride under controlled temperature conditions in the presence of a phosphorus-vanadium mixed oxide catalyst produced in a specified manner.
Although these prior art processes generally produce the desired catalyst, the commercial utility of a catalyst system and a catalytic process is highly dependent upon the cost of the catalyst employed, the conversion of the reactant(s), and the yield of the desired product(s). In many instances, a reduction in the costs of a catalyst system employed in a given process on the order of a few cents per kilogram or pound, or a small percent increase in the yield of the desired product represents a tremendous commercial economical savings and advantage. Accordingly, research efforts are continually being made to define new or improved catalyst systems and methods and process of making new and old catalyst systems to reduce the costs and/or upgrade the activity and selectivity of such catalyst systems in such processes. The discovery of the process of the instant invention, therefore, is believed to be a decided advance in the art.